report from Business Insider.
Clash of Clans is a free-to-play simulation game with tower defense elements, challenging players to build a village and defend it from frequent enemy attacks. While much of the game's content is accessible without additional purchases, players have the option of upgrading combat units and other in-game components by spending real-world money. The approach has proven popular among App Store customers, and Clash of Clans currently ranks as iTunes' single highest-grossing app as a result.
An App Annie report (via MCV) ranks Clash of Clans as the world's third-highest grossing free-to-play game, trailing GungHo's Puzzle & Dragons and King's Candy Crush Saga.